THE CAEBONrPEEOUS FLOEA. 167 



dinally ribbed and jointed stems so frequent in the ooal-formation, 

 and of which the common C. Suchovii is a typical form. The most 

 perfect of these stems represent the outer surface immediately within 

 the epidermis, in which case transverse lines or constrictions 

 mark the nodes, and at the nodes there are rounded spots, some- 

 times indicating radial processes of the pith, first described by 

 Williamson ; in other oases, the attachment of branohlets, or in some 

 specimens both. But some specimens show the outer surface of the 

 epidermis, in which case the transverse nodal lines are usually in- 

 visible, though the scars of branchlets may appear. In still other 

 examples the whole of the outer tissues have perished, and the so- 

 called Calamite is a cast of the interior of the stem, showing merely 

 longitudinal ribbing and transverse nodal constrictions. In study- 

 ing these plants in situ in the erect Calamite brakes of the coal- 

 formation of Nova Scotia, one soon becomes familiar with these ap- 

 pearances, but they are evidently unknown to the majority of palaeo- 

 botanists, though described in detail more than twenty years ago. 



When the outer surface is preserved it is sometimes seen to bear 

 verticils of long needle-like leaves (C Cistii), or of branchlets with 

 secondary whorls of similar leaves (C. Suelcovii and G. imdulatus). 

 No Calamite known to me bears broad one-nerved leaves like those 

 of Asterophyllites and Anrmlaria, though the larger stems of these 

 plants have been described as Calamites, and the term Calamocladus 

 has been used to include both groups. The base of the Calamite 

 stem usually terminates in a blunt point, and may be attached to a 

 rhizome, or several stems may bud out from each other in a group or 

 stool. The roots are long and cylindrical, sometimes branching. 

 The fruit consists of spikes of spore-cases, borne in whorls and sub- 

 tended by linear floral leaves. To these strobiles the name Calamo- 

 stachys has been given. 



Williamson has shown that the stem of Calamites consists of a 

 central pith or cavity of large size surrounded by a cylinder con- 

 sisting of alternate wedges of woody and cellular matter, with ver- 

 tical canals at the inner sides of the wedges, and slender medullary 

 rays. The thick cellular wedges intervening between the. woody 

 wedges he calls primary medullary rays; the smaller medullary 

 rays in the wedges, secondary medullary rays. There is thus a 

 highly complex exogenous stem based on the same principle with 

 the stem of a common Egwiaetum, but with much greater strength 

 and complexity. 



Williamson has also shown that there are different sub-types ol 

 these stems. More especially he refers to the three following : 



